In a year filled with red-soaked months, September may have been the worst for Paulson & Co.

The New York-based hedge fund suffered big losses in all of its hedge funds last month—including those that had, until now, bucked the trend and performed well. The firm's largest fund, Advantage Plus, fell almost 20% last month and is now down 47% on the year.

From the current issue of

We are accustomed to splitting trading into technical and fundamental buckets. Both involve crunching data; one set includes market fundamentals and the other pure price data. Alternative data is a third bucket that is gaining traction.